Study On Weak Gel Water - Based Drilling Fluid And Its Mechanism

The weal gel water-based drilling fluid is different from common colloidal dispersal frilling fluid system. It has special inner structure and rheological behavior with higher low shear rate viscosity(LSRV),which is usually used in large hole,horizontal wells and directional well for cutting transporting in the onshore and offshore oilfield of our country.But the field application and laboratory study of this type of drilling fluid indicates that the properties about salt resisting, temperature resisting (lower than120℃)was not enough,which can not be effectively used in the deep wells.therefor,it is imperative to develop and research on salt resisting and temperature resisting weal gel water-based drilling fluids technique.This article designs treating chemical’s molecular structure in the light of high temperature resisting active mechanism of treating chemical and chooses suitable reactive monomer AM/AMP and 2-acrylamideoctodecyl sulfonic acid (ASA)to composite water soluble polymers through free radical polymerization.The best synthetic condition is optimized after it is analyzed the effect of reaction conditions such as reaction temperature,initiator type and its amount,total concentration of monomer,monomer match,action time,pH on high temperature resisting and salt resisting performance of synthetic polymer gelling agent is synthetised through in-house experiment.Based on key additive of gelling agent,other additives are optimized to design a type of deep well clay-free weak gel water-base drilling fluid system which resist high temperature to 160℃.It is shown by result that,this type of drilling fluid based on synthesized fluid gelling agent has special rheological behavior with higher low shear rate viscosity(LSRV) and lower high shear rate viscosity(HSRV),and good performance in temperature resistance,salt resistance and calcium resistance,the effect of temperature on the rheology is less.Based on the observation and description of environmental SEM techniques and laser particle sizer analysis,the film forming agent and the temporary plugging agent play an important role in controlling the quality of filter cake,so as to reduce the filter loss.The microstructure of the gelling agent and weak gel drilling fluid and its active mechanism are analyzed through the method of microscopic experiments.The findings shows that the gelling agent can develop a good continuous three dimensional net microstructure both in fresh water and brine. Comparing with the gelling agent, the weak gel drilling fluid has more complex microstructure with continuous three dimensional net microstructure and sol grains in the net microstructure,which indicates the special characters of weak gel water-based drilling fluid. In combine with the performance parameters,the research also observes the influence of temperature,pH and CaCl2 on the net structure,the relationship between microstructure and structure performance and the performance of high temperature resting and salt resisting can be proved.